Effects of androgens on female sexual differentiation are often considered within a pathological context (e.g. ambiguous genitalia resulting from congenital adrenal hyperplasia), but in the spotted hyena a high androgen milieu during fetal development and sexual differentiation represents normal physiology, not pathology. Thus, the spotted hyena represents a unique system in which to study the effects of antenatal androgens on sexual differentiation. High androgen exposure in utero masculinizes female external genitalia to the extreme in spotted hyenas, but the effects of androgens on ovarian differentiation are not well studied. Specifically, androgens appear to increase the rate of follicular atresia in the developing ovary, which may explain the abundance of ovarian interstitial tissue and relative paucity of follicles in spotted hyenas. In the proposed research I will study a group of female hyenas that were previously exposed to anti-androgens while in utero. These females are now adults and the structure and function of their ovaries will be compared to that of untreated controls. The steroidogenic responsiveness of the ovaries to a gonadotropin challenge test will be assessed in vivo, as well as in vitro (after unilateral oophorectomy). Following oophorectomy, follicle number and steroidogenic enzyme activity will be measured, and steroid receptor levels will be quantified by immunocytochemistry. This research will improve our understanding of how prenatal exposure to androgens affects ovarian structure and function.